The availability and use of “Cloud” computing has expanded exponentially in the past few years. Under a conventional computing approach, users run software applications on their own computers and/or access software services hosted by local servers (such as servers run by a business enterprise). In contrast, under cloud computing the compute and storage resources are “in the cloud,” meaning they are physically hosted at a remote facility that is accessed via a computer network, such as the Internet. Compute and storage resources hosted by a cloud operator may be accessed via “services,” which are commonly referred to as cloud-based services, Web services or simply services.
Cloud-based services are typically hosted by a datacenter that includes the physical arrangement of servers that make up a cloud or a particular portion of a cloud. Data centers commonly employ a physical hierarchy of compute, network and shared storage resources to support scale out of workload requirements. FIG. 1 shows a portion of an exemplary physical hierarchy in a data center 100 including a number L of pods 102, a number M of racks 104, each of which includes slots for a number N of trays 106. Each tray 106, in turn, may include multiple sleds 108. For convenience of explanation, each of pods 102, racks 104, and trays 106 is labeled with a corresponding identifier, such as Pod 1, Rack 2, Tray 1B, etc. Trays may also be referred to as drawers, and sleds may also have various forms, such as modules and nodes. In addition to tray and sled configurations, racks may be provisioned using chassis in which various forms of servers are installed, such as blade server chassis and server blades.
Depicted at the top of each rack 104 is a respective top of rack (ToR) switch 110, which is also labeled by ToR Switch number. Generally, ToR switches 110 are representative of both ToR switches and any other switching facilities that support switching between racks 104. It is conventional practice to refer to these switches as ToR switches whether or not they are physically located at the top of a rack (although they generally are).
Each Pod 102 further includes a pod switch 112 to which the pod's ToR switches 110 are coupled. In turn, pod switches 112 are coupled to a data center (DC) switch 114. The data center switches may sit at the top of the data center switch hierarchy, or there may be one or more additional levels that are not shown. For ease of explanation, the hierarchies described herein are physical hierarchies that use physical LANs. In practice, it is common to deploy virtual LANs using underlying physical LAN switching facilities.
The cloud-hosted services are generally categorized as Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS). SaaS services, also commonly called Web services and cloud application services, enable access to services running on datacenter servers via a network connection and client-side interface, such as a Web browser. Well-known examples of SaaS services include e-mail Web services (e.g., Google gmail, Microsoft Hotmail, Yahoo mail), Microsoft Office 365, Salesforce.com and Google docs. PaaS, also known as cloud platform services, are used for applications and other development, while providing cloud components to software. Examples of PaaS include Amazon Web Services (AWS) Elastic Beanstalk, Windows Azure, and Google App Engine.
IaaS are services for accessing, monitoring, and managing remote datacenter infrastructures, such as computer (virtualized or bare metal), storage, networking, and networking services (e.g., Firewalls). Instead of purchasing and running their own physical hardware, users can purchases IaaS based on consumption. For example, AWS and Windows Azure respectively offer use of Amazon and Microsoft datacenter resources on a resource allocation/consumption basis. Amazon Elastic Compute Cloud (EC2) is a central part of AWS.
IaaS usage for a given customer typically involves allocation of data center resources. For example, a typical AWS user may request use of one of 24 different EC2 instances, which range from a t2.nano instance with 0.5 Gigabyte (GB) of memory, 1 core/variable cores/compute units and no instance storage to an hs1.8xlarge with 117 GB of memory, 16/35 cores/compute units and 48000 GB of instance storage. Each allocated EC2 instance consumes certain physical datacenter resources (e.g. compute, memory storage). At the same time, datacenter racks may support a multitude of different configurations. To maximum resource allocation, the IaaS operator needs to track what resources are available in which rack.